1. Field of the Invention
The present invention relates to a solar tracker used to direct solar energy.
2. Description of Related Art
Electrical power systems that operate on fossil fuels create environmentally harmful by-products. For this reason there has been developed alternate fuel systems to generate electricity. U.S. Pat. No. 4,536,847 issued to Erickson et al., discloses a concentrator solar conversion system that converts solar energy into electric power. The concentrator system has a plurality of trackers that each have reflective surfaces which reflect solar energy to a single focal point. Located at the focal point is a receiver unit which converts the solar energy into electrical power.
The reflective surfaces are rotated to track the movement of the sun so that the reflected solar energy is always focused on the receiver. The reflective surfaces are moved by motors that are controlled by a computer. The trackers are typically connected to the computer and a power supply by field wires.
The receiver typically has a heat exchanger which becomes heated by the reflected solar energy. The heat is transferred to a working fluid that drives a device such as a turbine or sterling engine. The turbine converts the thermal energy into mechanical energy, which is then converted into electrical energy by a generator. The working fluid also functions as a coolant that reduces the temperature of the receiver. If the flow of working fluid is terminated, the solar energy will quickly overheat and melt the receiver. In such a situation, it is desirable to move the trackers to a standby position so that solar energy is not directed toward the receiver. For example, lightning may strike and damage the power distribution system. Without power, the tracker is unable to move to the standby position. It would therefore be desirable to provide a self-sufficient tracker that can independently move the position of the reflective surfaces.
The reflective surfaces are typically rotated about a gimbal. The gimbal has an incremental encoder that provides feedback signals which are used to determine the relative position of the reflective surfaces. When power is terminated to the tracker, the reflective surfaces must be moved back to an initial reference position to reinitialize the system. Because of the relatively low slew rate of the tracker motor, this process can take up to 20-40 minutes. It would be desirable to reduce the time required to obtain a reference position of the trackers . It would also be desirable to improve the accuracy of a solar tracker to optimize the energy conversion efficiency of a solar energy system.